Band-pass filter arrangement



July 2, 1940. E. KLOTZ BAND PASS FILTER ARRANGEMENT Filed Jan. 13, .1937

LOOSE (OZ/PIE [0W DAMP/N6 1005f COUPLE ll/Gl/ DAMP/N6 DAMP/1V6RES/STANCE lNVENTOR ERNST KLOTZ 62 ATTORNEY Patented July 2, 1940 PATENTOFFlCE BAND-PASS FILTER ARRANGEMENT Ernst Klotz, Berlin, Germany,assignmfnnken Gcscllechaft fiir m. b. H., Berlin, Germany to Tele-Drahtlose Telegraphic Germany, a corporation of Application January 13,1937, Serial No. 120,342 In Germany January 25, 1936 2 Claims.

Modern receiver sets are provided with an operating knob designed toadjust the receiver set so that it will either operate at will foroptimum reproduction (quality) or high selectance. In order that not toomuch selection may be lost in the attempt to secure high qualityreproduction, it is preferable that not only the damping be changed, butat the same time also the coupling. An increase in the damping isadvantageous when the coupling is close, because in this manner an unduecrevass of the resonance curve is prevented. In the prior art it hasbeen customary to occasion a change in the damping by cutting in orchanging a resistance, or else by the shifting of a supplemental dampingwinding.

In an arrangement designed to change the band width of a band-passfilter according to the invention, a damping winding or turn being fixedfor a definte frequency is disposed in such a manner that the couplingrelation between the rotatable or pivotal coil and the said winding orturn is rendered closer or stronger when the coupling with the othercoil becomes closer.

The present invention will be explained more fully by reference to theaccompanying drawing wherein,

Fig. 1 illustrates in schematic form a pair of coils in uncoupledcondition;

Fig. 2 illustrates the same arrangement but with the coils in coupledcondition;

Fig. 3 is a schematic side view of the arrangement shown in Fig. 2;

Fig. 4 illustrates diagrammatically a unit made up in accordance withthe present invention; and,

Fig. 5 illustrates in diagrammatic form a use for the unit shown in Fig.4.

Referring now to Fig. 1 it will be seen that the two coils both of whichare provided with cores are arranged so that their axes are at rightangles to one another. A short-circuited turn R in conjunction with aresistor W are shown alongside of the lower coil structure. In Fig. 2 itwill be seen that the lower coil has been rotated so that its axis isnow parallel with the axis of the upper coil. These coils are now shownin close coupled condition.

In the arrangement illustrated in Fig. 4, the band-pass filter is builtinto a shielding cylinder. The damping turn or ring R is attached. tothe insulation plate Pl by the aid of two rods St, the said insulationplate serving also as a support for the top coil and the rotatable lowercoil.

The coils are disposed dissymmetrically inside the cylinder. This schemehas been adopted for be possible to use a a definite object. Beforeplained in more detail, understoodzi The looser the coupling between thedamping turn and the revoluble coil (in Fig. 1), the lower must be theresistance W which is cut in the circuit, if the desired damping is tobe secured. Inasmuch as the ratio between the inductance and ohmicresistance of the damping turn becomes then increasingly greater, thereoccurs more detuning of the rotatable coil. In other words, it is mostfavorable to make the coupling of the damping turn close and to choosethe damping resistance high. However, in practice this is possible onlyto a certain extent inasmuch as the rotatable coil requires a certainamount of space for which reason the damping turn and the rotatable coilmust be mounted a certain distance apart. For this reason, a certaindetuning will arise, that is, the inductance declines with closercoupling.

In this connection, there arises another action which has a favorableeffect. In the arrangement Fig. 4, without a damping turn, provided thecoils are disposed in the middle of the shielding cylinder, theinductance of the rotatable coil decreases as the coupling becomesstronger seeing that the short-circuit currents in the shield are madeto flow over a longer path. Now, in order that such an increase in theinductance may be prevented the rotatable coil according to theinvention is so mounted that, as the coupling with the other coil isstrengthened, also the coupling with the shield becomes stronger, withthis consequence that the inductance is stabilized and preserved.

If a damping ring or turn R is provided th is no need for disposing therotatable coil equally dissymmetrically seeing that, with closercoupling with the damping ring, the inductance will in part be balancedagain as a result of the longer path in the shield.

Fig. 5 illustrates a Way in which the unit shown in Fig. 4 may beconnected in a band pass filter circuit. The input terminals 4 and 5 ofthe band pass circuit are connected to a suitable source of signalenergy and the output terminals 6 and 1 to a utilizing device. It willbe noted that the coils I and 2 are variably coupled and that theshort-circuited turn 3 is variably coupled to the coil 2. Variations ofone coupling also vary the other as shown by the uni-control 8.

In lieu of a short-circuiting ring it would also circuit presenting therequisite amount of damping and being tuned to the the latter is to beexthe following must be frequency of the oscillation circuits of thebandpass filter. What happens in this case is no detuning, but merely adamping.

The present invention is useful not only in connection with band-passfilters with fixed tuning, but also with band-pass filters designed foradjustable tuning, for instance, input band-pass filters in receiverapparatus. In order that for different frequencies the proper amonut ofdamping may be secured, the damping ring may ice moved as a function ofthe tuning. It is also feasible to vary the damping resistance W as afunction of the tuning. What may also be mentioned is that the inventionis not confined to an arrangement of the coil as shown in theaccompanying drawing, in fact, that it is also useful in cases where theaxial positions are different.

What I claim is:

1. In radio signalling apparatus, a band pass circuit including a firstcoil fixedly mounted within a shielding container, a second coil movablymounted within the shielding container between a position where the axesof the coils are parallel and a position where the axes thereof areperpendicular to each other, a closed circuit including resistance andan auxiliary coil fixedly mounted within said container said auxiliarycoil being in coupling relationship with said movable coil wherebyadjustments of the movable coil simultaneously varies the couplingbetween it and the first coil and the damping.

2. In radio signalling apparatus, a band. pass circuit including a pairof coils mounted in coupling relationship within a shielding container,damping means mounted adjacent one of said coils and comprising a closedcircuit including resistance and a coil, means for adjusting theposition of one of said coils with respect to the other and to saidclosed circuit to thereby simultaneously vary the coupling between thetwo coils and between the last named one of said coils and the closedcircuit whereby the amount of damping of said band pass circuit isvaried simultaneously with variations in coupling between said pair ofcoils.

ERNST KLOTZl

